We usually go to DL at least once a year and have done both the Supershuttle and the Airport Bus. Here's my opinion for what it's worth!
Both pick up in the same area at LAX. You have to have your bags and be waiting on the curb, outside.
Supershuttle is just a little more expensive but will take you right to your hotel front door. Depending on where your hotel is, the airport bus may only drop you on the street within about a block of your hotel, especially if your hotel is on Harbor Blvd. or another busy street (some kind of new law about the buses tying up traffic or something). This means that you have to haul all your luggage by yourself to your hotel. This also means that you have to haul it all back to the bus stop, and be there waiting for the bus at the right time. This may not be a problem if you are a light packer, don't have small kids in tow, and it isn't 95 degrees out, etc.
The shuttle is nice because they pull up right to the front door of your hotel and will load and unload your luggage (you can wait in air conditioning at your leisure). They will always try to pack as many people into the shuttle as possible which means you make a few stops. This isn't too bad if you're not in a hurry, as you get a little tour on the way.
(The bus also makes several stops, but they are all within the same area around DL, vs. the shuttle which could be anywhere between LAX and DL.)
In my experience, both the bus and the shuttle drivers drive fast and like bats out of you know where, and being on a nice big bus is somewhat comforting as you know you are in one of the biggest vehicles on the road if there were to be an accident.
If you can afford it, fly into and out of John Wayne/Orange Co. airport and take a taxi. (it's only about 15 min. max this way) however all the good travel specials only seem to deal with LAX.
Bottom line (in my opinion), six of one, half dozen of the other. You pay a little more for the shuttle, but you get a little more convienience.
